Synergistic mixture of adiamine and alkalimetalamide as an antioxidant composition and lubricants containing same

ABSTRACT

Antioxidant composition comprises a synergistic mixture of a diamine, e.g. N,N,N&#39;&#39;-tris-(4-t-octylphenyl)-4-t-octyl-1,2phenylene diamine, di-DODPA, and an alkali metal derivative of the same or similar diamine. The composition is particularly suitable for use in synthetic ester lubricants.

United States Patent Bird et al.

May 6, 1975 SYNERGISTIC MIXTURE OF ADIAMINE AND ALKALIMETALAMIDE AS AN ANTIOXIDANT COMPOSITION AND LUBRICANTS CONTAINING SAME Inventors: Michael Gavin Bird, Weybridge;

Keith Aled Wyn Parry, Camberley, both of England Assignees The British Petroleum Company Limited, London, England Filed: Jan. 5, 1972 Appl. No.: 215,646

Foreign Application Priority Data Jan. I8, I97] United Kingdom... 2350/71 Aug. I2, 197i United Kingdom.... 37868/7] Sept. 7, 1971 United Kingdom 4IS89/7l US. Cl 252/49.7; 252/50; 252/400 R;

252/401 Int. Cl Cl0n 1/10 Field of Search 252/497, 50, 400 R, 401

References Cited UNITED STATES PATENTS 4/1966 Oberright et al. 252/50 X FOREIGN PATENTS OR APPLICATIONS l,047,278 lI/l966 United Kingdom 252/50 655,985 l/l963 Canada 252/491 OTHER PUBLICATIONS Primary ExaminerPatrick P. Garvin Assistant Examiner-Andrew H. Metz Attorney, Agent, or Firm-Morgan, Finnegan, Durham & Pine [57] ABSTRACT Antioxidant composition comprises a synergistic mixture of a diamine, e.g. N,N,N'-tris-(4-t-octylphenyl )-4- t-octyl-l,2-phenylene diamine, di-DODPA, and an alkali metal derivative of the same or similar diamine. The composition is particularly suitable for use in synthetic ester lubricants.

I4 Claims, N0 Drawings SYNERGISTIC MIXTURE OF ADIAMINE AND ALKALIMETALAMIDE AS AN ANTIOXIDANT COMPOSITION AND LUBRICANTS CONTAINING SAME This invention relates to high temperature antioxidants and to libricants containing them, particularly synthetic lubricants suitable for use under the severe high temperature conditions that exist in the operation of modern aero gas turbine engines.

The problem of thermal stability in aero gas turbine lubricants can be satisfactorily handled by the use of certain hindered ester basestocks which generally also have good low temperature properties, being fluid in many cases at temperatures of 40 or below. A more difficult problem that has to be faced however, is the problem of oxidation stability and resistance to corrosion which arises owing to the fact that the lubricants have to operate at high bulk oil temperatures (about 200C) in contact with air. These conditions have the effect of greatly accelerating the oxidative deterioration of the lubricant which generally results in an increase in its viscosity and acidity, and corrosion of, or formation of deposits on, metal surfaces. Excessive increase in viscosity can lead to a restricted flow of lubricant to the engine bearings resulting in inadequate lubrication on starting and/or inadequate cooling during engine running. Deterioration of engine component condition by excessive corrosion or deposition can lead to malfunctioning of the moving parts, and excessive formation of oil-insoluble materials can cause inadequate lubrication due to blockage of oil-ways. It is therefore very desirable that a lubricant of this type should show no more than a slight tendency to increase in viscosity and acidity during service.

The performance of a lubricant in these respects is frequently assessed by submitting it to an accelerated oxidation/corrosion test in which a sample of oil is maintained at a high temperature in contact with metal test pieces while a stream of air is bubbled through it for a prolonged period of time. Forms of this test are quoted in some Government and Engine Manufacturers specifications for aero gas turbine lubricants. In one form of this test, used to assess oils for high temperature applications, the sample size is 90 grams, a temperature of 400F (204C), an air flow rate of 5 litres/- hour and a test period of 72 hours are adopted as the test conditions, and one inch square plates of magnesium alloy, aluminium alloy, copper, silver and steel are used as the metal test pieces. A variation of this procedure uses a temperature of 425F (218C) and a test period of 48 hours. In these forms of the test, oils having poor resistance to oxidation at high temperatures give high viscosity and acidity increase and tend to corrode certain of the metals, especially copper and magnesium.

Various antioxidants are known for alleviating the above problems but in producing a final lubricant blend it is important that the particular combination of base oil and additives used should be clean in use and not give rise to unacceptable levels of deposits on the engine components. The above-mentioned oxidation tests assess the cleanliness of an oil in this respect by measuring the amount of insoluble material formed.

An object of the present invention is to provide a high temperature antioxidant which is capable of imparting outstanding oxidation stability to lubricating oils intended for the lubrication of moderm aero gas turbine engines, and which is clean in use.

In U.S. Pat. application Ser. No. l64,946 filed July 21, l97l there is disclosed a diamine of formula wherein A is a benzene nucleus substituted in the para position with a tertiary alkyl group having 4 to 9 carbon atoms and B is A or an alpha or beta naphthyl group. A process for the preparation of such a diamine is also disclosed. There is provided in the aforementioned application Ser. No. 164,946 a process for the production of a diamine of Formula I.

which process comprises thermally rearranging a hydrazine of Formula II N N (II) wherein X is a benzine nucleus substituted in the para position with a tertiary alkyl group having 4 to 9 carbon atoms and Y is X or an alpha or beta naphthyl group.

By way of example, preparation of N,N,N'tris-(4-toctylphenyl)-4-octyl-l,Z-phenylene diamine, subsequently referred to as the diamine is as follows:

394 g (1 mole) of 4,4'-dioctyldiphenyl amine were dissolved in 4 litres of acetone in a 5 litre beaker.

158 g (1 mole) of crystalline potassium permanganate were dissolved in 400 mls of distilled water at 80C and added over the course of an hour to the amine solution, the mixture being heated to 50C and stirred continuously. During the addition, manganese dioxide and N,N'-tetra-tris(-4-octylphenyl) hydrazine were precipitated. The complete mixture was stirred for a further 60 mins, after which time the precipitate was filtered off through a Buchner funnel and washed once with the filtrate. When the residue in the funnel was dry it was dissolved in 2 litres of toluene and the inorganic insolubles filtered from the solution. The toluene was then distilled under vacuum at 80C in a rotary evaporation to give the solid hydrazine.

The powdered hydrazine was melted and maintained at 106C for 20 hours. Upon cooling, the solid antioxidant was ground to a yellow crystalline solid.

Analysis of the solid antioxidant by thin layer chromatography revealed that is consisted of a mixture of monamine (15%), diamine and triamine (15%).

and (b) an alkali metal derivative of an amine of for mula where x and y are as previously defined and n is O, l or 2.

According to one preferred feature the amine of For mula 11 is of Formula i.e., n is 0, and the alkali metal derivative is prepared by reacting the alkali metal with the amine.

According to another preferred feature, the amine of Formula 11 in again of Formula and the alkali metal derivative in this case is prepared by reacting the alkali metal hydride with the amine.

According to yet another preferred feature the amine of Formula 11 is a diamine of Formula i.e., n is l. The alkali metal derivative may be prepared by reacting the diamine with an alkali metal or alkali metal hydride.

Suitable diamines of Formula 1 may be prepared by the method disclosed in Ser. No. 164,946 from 4,4'-dit-butyl diphcnylamine, (DODPA) 4,4-di-t-hexyldiphenylamine', N [4-t-butyl-phenyl]-a-naphthylamine; N [4-t-octyl-phenyl]-a-naphthylamine; N[4t-butyl- 4 phenyll-B-naphthylaminc; NH-t-octyl phenyH-B- naphthylamine, and, preferably, 4,4'-di-t-octyl diphenylamine.

The preferred diamine is N, N, N tris -(4toctylphenyl)-4t-octyl-1,Z-phenylene diamine (di- DODPA).

Diamines prepared by this method may have small amounts of monoamines and triamines associated with them.

Suitable amines of Formula ll are those listed previously as suitable for conversion to diamines and also the diamines and triamines resulting from such conversions.

The alkali metal derivatives of the amine of Formula 11 may be prepared by reacting the alkali metal or metal hydride with an excess of the amine at a temperature in the range to 200C.

The preferred alkali metals are potassium and sodium.

The invention also includes a lubrication composition comprising a lubricating base oil, which may be mineral or synthetic, and up to 10% by weight of an antioxidant composition as described above.

The lubricating composition suitably contains between 00] and 6% by weight of the diamine, preferably between 2 and 4%. The lubricating composition suitably contains between 0.01 and 0.5% by weight of the alkali metal derivative, preferably between 0.04% and 0.2%.

The effect of the antioxidant composition is shown to maximum advantage by using it in a thermally stable liquid neutral polyester basestock. Such polyesters are prepared by reacting together under esteriflcation conditions and in one or more stages:

i. an aliphatic monoand/or polyhydric alcohol having 5-15, preferably 510, carbon atoms per molecule and having no hydrogen atoms attached to any carbon atom in a 2 position with respect to any OH group and ii. an aliphatic mono and/or polycarboxylic acid having 2-14, preferably, 3-12 carbon atoms per molecule.

By polyester is meant an ester having at least two ester linkages per molecule; it therefore includes diesters such as neopentyl glycol dipelargonate and di(2:2:4-trimethylpentyl) sebacate. The term neutral is used to mean a fully esterified product.

It is to be understood that in the esterification reaction described above there may be used more than one of any of the reactants mentioned eg. a mixture of monocarboxylic acids and, in any case, the neutral ester product of the esterification reaction will sometimes consist of a mixture of different ester molecules, so the expression polyester is to be construed in this light.

Examples of suitable acids and alcohols that may be used in the preparation of the polyester are caprylic acid, capric acid. caproic acid, enanthic acid, pelargonic acid, valeric acid, pivalic acid, propionic acid, azelaic acid, 2:2:4-trimethylpentanol, neopentyl alcohol, neopentyl glycol, trimethylolethane, trimethylolpropane, pentaerythritol and dipentaerythritol.

Suitable polyesters are in the esters of trimethylolpropane, trimethylolethane, pentaerythritol and/or dipentaerythritol with one or more monocarboxylic acids having 3 to 10 carbon atoms, particularly one or more of those mentioned in the previous paragraph.

Most suitably, the trimethylolpropane and dicarboxylic acid are reacted in the molar ratio of 1:0.05/- O.75, preferably 110.075 0.4, the amount of monocarboxylic acid being sufficient to provide a carboxyl/hydroxyl balance in the reactants.

The invention is illustrated by the following examples EXAMPLE 1 A potassium derivative of 4,4'-di-t-octyl diphenylamine (DODPA) was prepared by reacting 2g potassium with 100g of the amine at 190C.

Two blends were then prepared using a synthetic ester basestock and subjected to the Rolls Royce 1001 oxidation test.

Air saturated with water vapour was bubbled at the rate of 250 ml/min through 50 ml samples of the blends at elevated temperature for 192 hours.

Deterioration of the samples because of oxidation were then measured in terms of fluid loss, acidity and viscosity change, and toluene insoluble materials after topping up the tested samples to their original volume with fresh material. The following results were obtained.

Panel Further samples of the blends were subjected to the Pratt and Whitney oxidation test.

A 90g. sample of each blend was taken and in it were The cleanliness of the compositions was further as sessed by the Roxana Panel Ccaker Test in which a sample of the blend containing diamine (di DODPA) K DODPA was splashed on to a weighed aluminium panel heated at 600F for 8 hours and the nature and weight of the deposit on the panel were noted.

The following results were obtained:

Panel Description Deposit Mg. Coverage Type of deposit 4.0 50 Sticky pale yellow The ester basestock was a complex ester prepared by tive of 4.4'-di-t-octyl diphenylamine.

EXAMPLE 2 200g of 4,4-di-t-octyldiphenylamine (DODPA) were melted in a round bottomed flask at about 100C and the flask was flushed out with nitrogen gas. 6g of sodium hydride (ie. 12g of a 50% oil dispersion of sodium hydride) were added gradually to the stirred diphenylamine over a period of two hours. The reaction was vigorous and the contents of the flask turned dark green in colour. The product was heated and stirred for ergist was ready for use without any further treatment.

Two blends were then prepared using a synthetic ester basestock and subjected to the Rolls Royce 1001 oxidation test.

The following results were obtained:

Temp. 74 Fluid A KV A TAN toluene Additive Package "C Loss at 2 IUF mgKOH/g insols.

4% diamine i. 230 Gelled after 100 hours 4% diamine 0.04% NaH/DODPA 230 (16.0 160.4 2.6 Nil reaction product The ester basestock was a complex ester prepared by esterifying caprylic acid; l,l ,l-trimethylol propane and sebacic acid in the molar ratio of 28:10zl.

A potassium synergist was prepared by melting 30g. N,N,N'-tris(4t-octylphenyl)-4t-octyl-1,2-phenylene diamine under nitrogen in a flask. 0.4g metallic potassium was added and heating continued for 3 hours. The reaction product was then cooled and comminuted.

A KV A TAN Sludge 7r FLuid Metal Weight Change Blend at F mg KOH/g mg Loss Mg Al Cu Ag Fc Estcr basestock 16.8 1.] Nil 2.4 Nil Nil -U.06 O.U2 ().()4 4% by wt. diaminc Ester basestock 16.2 3.5 5.3 1.9 Nil Nil 0.(]5 +0.06 +0.06

4% by wt. diaminc 0.04% by wt. K DODPA A sodium synergist was prepared by reacting 16.3g of H the diamine with lg of a 50% oil dispersion of sodium l hydride in hexane. After 2 hours refluxing the hexane X N Y N X solution was filtered to remove excess sodium hydride.

The hexane was then stripped and the synergist cooled X and comminuted.

Various blends were then prepared using synthetic ester basestocks and subjected to the Rolls Royce 1001 oxidation test.

The following results were obtained: and

Temp "/1, Fluid A kv A Tan 71 Toluene Example Additive Package Basestock C Loss at 2IUF mg KOH/g lnsolubles 3 4% diamine Ester A 225 Gellcd after 100 hours 4 4'4 diamine Ester A 230 64.2 50 L4 Nil 0.04% K diamine 5 4% diamine Ester A 235 711.8 Gcllcd after 190 hours (1.04% K diamine 6 6% diamine Ester A 230 55 40.4 0.7 Nil (1.06% K diamine 7 6% diamine Ester A 235 77.2 103.6 1.65 Nil (106 K diamine ti 4% diamine Ester B 225 Gcllcd after lOU hours 9 6% diamine Ester B 230 62.6 34.8 (1.3 Nil [1,06% K diamine i0 (1% diamine Ester B 235 77.2 50.7 0.55 Nil 006% K diamine l l 4% diamine 0.04% Na derivative Ester A 230 71.4 190 2.75 Nil K diamine potassium derivative of the diamine Na diamine sodium dcri\ alive 01' the diamine Ester A was a complex ester prepared by esterifying b. an alkali metal amide of an amine of the formula I H caprylic acid, l,1,1,-trimethylol propane and sebaelc acid in the molar ratio of 28:10:l. Y N Y N x Ester B was prepared by esterifying monopentaerythritol with a mixture of normal alkanoic acids of chain x n length C having an average chain length of C Further blends were subjected to the Pratt and Whitney oxidation test.

The following results were obtained. (11) Example Additive Package Basestock Fluid 7: A kv A TAN Sludge Metal Weight Change Loss at Mill"? mgKOH/g mg Mg Al Cu Ag Fe 12 3% DODPA 0.5% Ester A 2.3 31.2 5.0 1.9 0.02 +0.02 +0.01 +0.03 +0.03

OPANA l3 4% diamine Ester A 3.2 12.3 0.5 7.9 (J.0l (].UI -{).l3 -0.02 l]1Ol 0.04% K diamine +03% PL 297 I4 4% diamine Ester B 2 l 12 5 0.6 3.1 (J.()] -(J.U3 41.13 -().O2 +0.07

0.04% K diamine +03% PL 297 PL 297 a salt of salicylaminoguanidine and one or more C fatty acids DODPA 4,4-dioctyldiphcnylaminc OPANA 4-oct lphenyl-u-naphthylamim:

where X is a benzene nucleus substituted in the para position to the nitrogen atom with a tertiary alkyl group having 4 to 9 carbon atoms and Y is selected from the group consisting of a benzene nucleus substituted in the para position with a tertiary alkyl group having 4 to 9 carbon atoms, an alpha naphthyl group and a beta naphthyl group, and n is 0, l, or 2, the weight ratio of the diamine of Formula 1 to the alkali metal amide being 121 to 12:1.

2. An antioxidant composition according to claim 1, wherein n is O and the alkali metal amide is prepared by reacting an alkali metal with the amine of Formula II in the presence of an excess of said amine at a temperature in the range of l50 to 200C 3. An antioxidant composition according to claim 1 wherein n is and said alkali metal amide is prepared by reacting an alkali metal hydride with an excess of the amine of Formula II at a temperature in the range 150 to 200C.

4. An antioxidant composition according to claim 1 where n is l.

5. A lubricating composition comprising a lubricating base oil and up to l0% by weight of an antioxidant composition according to claim 1.

6. A lubricating composition according to claim wherein the diamine of Formula I is present in an amount in the range 0.01 to 6% by weight.

7. A lubricating composition according to claim 6 wherein the diamine is present in an amount in the range 2 to 4% by weight.

8. A lubricating composition according to claim 5 wherein the alkali metal amide is present in an amount in the range 0.01 to 0.5% weight.

9. A lubricating composition according to claim 8 wherein the alkali metal amide is present in an amount in the range 0.04 to 0.2% by weight.

10. A lubricating composition comprising a synthetic polyester base oil and up to 10% by weight of an antioxidant composition according to claim 1.

11. An antioxidant according to claim I, wherein the diamine is N,N,N-tris-(4-t-octylphenyl)-4-t-octyl-l,2- phenylene diamine.

12. An antioxidant according to claim 2, wherein the amine of Formula ll is 4,4'-di-t-butyl-diphenylamine; 4,4-di-t-hexyl-diphenylamine; N [4t-buty1phenyl]-anaphthylamine; N [4-t-octylphenyl]-a-naphthylamine;

N [4-t-butylphenyl]-B-naphthylamine; N [4-toctylphenyll- -naphthylamine or 4,4'-di-t-octyldiphenylamine.

octyl-diphenylamine. 

1. AN ANTIOXIDANT COMPOSITION COMPRISING A. A DIAMINE OF THE FORMULA
 2. An antioxidant composition according to claim 1, wherein n is 0 and the alkali metal amide is prepared by reacting an alkali metal with the amine of Formula II in the presence of an excess of said amine at a temperature in the range of 150* to 200*C.
 3. An antioxidant composition according to claim 1 wherein n is 0 and said alkali metal amide is prepared by reacting an alkali metal hydride with an excess of the amine of Formula II at a temperature in the range 150* to 200*C.
 4. An antioxidant composition according to claim 1 where n is
 1. 5. A lubricating composition comprising a lubricating base oil and up to 10% by weight of an antioxidant composition according to claim
 1. 6. A lubricating composition according to claim 5 wherein the diamine of Formula I is present in an amount in the range 0.01 to 6% by weight.
 7. A lubricating composition according to claim 6 wherein the diamine is present in an amount in the range 2 to 4% by weight.
 8. A lubricating composition according to claim 5 wherein the alkali metal amide is present in an amount in the range 0.01 to 0.5% weight.
 9. A lubricating composition according to claim 8 wherein the alkali metal amide is present in an amount in the range 0.04 to 0.2% by weight.
 10. A lubricating composition comprising a synthetic polyester base oil and up to 10% by weight Of an antioxidant composition according to claim
 1. 11. An antioxidant according to claim 1, wherein the diamine is N,N,N''-tris-(4-t-octylphenyl)-4-t-octyl-1,2-phenylene diamine.
 12. An antioxidant according to claim 2, wherein the amine of Formula II is 4,4''-di-t-butyl-diphenylamine; 4,4''-di-t-hexyl-diphenylamine; N (4-t-butylphenyl)- Alpha -naphthylamine; N (4-t-octylphenyl)- Alpha -naphthylamine; N (4-t-butylphenyl)- Beta -naphthylamine; N (4-t-octylphenyl) - -naphthylamine or 4,4''-di-t-octyl-diphenylamine.
 13. An antioxidant composition according to claim 4, wherein the amine of Formula II is N,N,N''-tris-(4-t-octyl-1,2-phenylene diamine.
 14. An antioxidant composition in accordance with claim 1, wherein the diamine of Formula I is a diamine obtained from a thermal conversion of an amine selected from the group consisting of 4,4''-di-t-butyl-diphenylamine; 4,4''-di-t-hexyl-diphenylamine; N(4-t-butylphenyl)- Alpha -naphthylamine; N(4-t-octylphenyl)-Alpha -naphthylamine; N(4-t-butylphenyl)- Beta -naphthylamine; N(4-t-octylphenyl)- Beta -naphthylamine and 4,4''-di-t-octyl-diphenylamine. 